# JavaScript

When creating workflows, you'll often need to write dynamic expressions. This page provides an overview of enabling JavaScript expressions and what functions and objects you can use.

## Installing the JavaScript Feature

The JavaScript Expressions feature is provided by the following package:

```bash
dotnet add package Elsa.Expressions.JavaScript
```

You can enable the feature as follows:

{% code title="Program.cs" %}

```csharp
services.AddElsa(elsa =>
{
   elsa.UseJavaScript();
});
```

{% endcode %}

### Configuration

The `UseJavaScript` extension provides an overload that accepts a delegate that lets you configure `JintOptions`. These options let you configure the underlying [Jint](https://github.com/sebastienros/jint) engine.

For example:

{% code title="Program.cs" %}

```csharp
services.AddElsa(elsa =>
{
   elsa.UseJavaScript(options =>
   {
      options.AllowClrAccess = true;
      options.RegisterType<Order>();
      options.ConfigureEngine(engine =>
      {
         engine.Execute("function greet(name) { return `Hello ${name}!`; }");
         engine.SetValue("echo", (Func<string, string>)(s => "Echo: " + s));
      });
   });
});
```

{% endcode %}

{% hint style="info" %}
Elsa uses [Jint](https://github.com/sebastienros/jint) to implement the JavaScript expression evaluator.
{% endhint %}

## Globals

The following functions and objects are available as globals to all JavaScript expressions:

* [JSON](#json)
* [variables](#variables)
* [getWorkflowDefinitionId](#getworkflowdefinitionid)
* [getWorkflowDefinitionVersionId](#getworkflowdefinitionversionid)
* [getWorkflowDefinitionVersion](#getworkflowdefinitionversion)
* [getWorkflowInstanceId](#getworkflowinstanceid)
* [setCorrelationId](#setcorrelationid)
* [getCorrelationId](#getcorrelationid)
* [setVariable](#setvariable)
* [getVariable](#getvariable)
* [getInput](#getinput)
* [getOutputFrom](#getoutputfrom)
* [getLastResult](#getlastresult)
* [isNullOrWhiteSpace](#isnullorwhitespace)
* [isNullOrEmpty](#isnullorempty)
* [parseGuid](#parseguid)
* [newGuid](#newguid)
* [newGuidString](#newguidstring)
* [newShortGuid](#newshortguid)
* [bytesToString](#bytestostring)
* [bytesFromString](#bytesfromstring)
* [bytesToBase64](#bytestobase64)
* [bytesFromBase64](#bytesfrombase64)
* [stringToBase64](#stringtobase64)
* [stringFromBase64](#stringfrombase64)
* [streamToBytes](#streamToBytes)
* [streamToBase64](#streamToBase64)
* get{InputName}
* get{VariableName}
* set{VariableName}

### JSON

The `JSON` type provides static methods to parse JSON strings into JavaScript objects and to serialise JavaScript objects into JSON strings.

```javascript
// Serialize the specified value as a JSON string.
JSON.stringify(object value);

// Deserialize the specified JSON string into a JavaScript object.
JSON.parse(string json);
```

### variables

The `variables` object provides static access to the workflow variables. For example, if your workflow has a variable called OrderId, you can get and set that workflow variable using the following JavaScript expression:

```javascript
// Set the OrderId workflow variable.
variables.OrderId = newGuid();

// Get the OrderId workflow variable.
const orderId = variables.OrderId;
```

### getWorkflowDefinitionId

Returns the workflow definition ID of the currently executing workflow.

```javascript
getWorkflowDefinitionId(): string;
```

### getWorkflowDefinitionVersionId

Returns the workflow definition version ID of the currently executing workflow.

```javascript
getWorkflowDefinitionVersionId(): string;
```

### getWorkflowDefinitionVersion

Returns the workflow definition version of the currently executing workflow.

```javascript
getWorkflowDefinitionVersion(): number;
```

### getWorkflowInstanceId

Returns the workflow instance ID of the currently executing workflow.

```javascript
getWorkflowInstanceId(): string;
```

### setCorrelationId

Sets the correlation ID of the currently executing workflow to the specified value.

```javascript
setCorrelationId(value: string);
```

### getCorrelationId

Gets the correlation ID of the currently executing workflow.

```javascript
getCorrelationId(): string?;
```

### setVariable

Sets the specified workflow variable by name to the specified value.

```javascript
setVariable(name: string, value: any);
```

### getVariable

Gets the specified workflow variable's value by name.

```javascript
getVariable(name: string): any;
```

### getInput

Gets the specified workflow input by name.

```javascript
getInput(name: string): any;
```

### getOutputFrom

Gets the specified activity output by name from the specified activity by name.

```javascript
getOutputFrom(activityIdOrName: string, outputName?: string): any;
```

### getLastResult

Gets the output of the last activity that executed.

```javascript
getLastResult(): any;
```

### isNullOrWhiteSpace

Returns `true` if the specified string is null, empty or consist only of whitespace characters, `false` otherwise.

```javascript
isNullOrWhiteSpace(string? value): boolean;
```

### isNullOrEmpty

Returns `true` if the specified string is null or empty, `false` otherwise.

```javascript
isNullOrEmpty(string? value): boolean;
```

### parseGuid

Parses the specified string into a `Guid`.

```javascript
parseGuid(string value): Guid;
```

### newGuid

Creates a new `Guid`.

```javascript
newGuid(): Guid;
```

### newGuidString

Creates a new `Guid` as a `string` representation.

```javascript
newGuidString(): string;
```

### newShortGuid

Creates a new short GUID as a `string` representation.

```javascript
newShortGuid(): string;
```

### bytesToString

Converts a byte array to a string.

```javascript
bytesToString(buffer: byte[]): string;
```

### bytesFromString

Converts a string to an array of bytes.

```javascript
bytesFromString(value: string): byte[];
```

### bytesToBase64

Converts a byte array to a base64 string.

```javascript
bytesToBase64(buffer: byte[]): string;
```

### bytesFromBase64

Converts a base64 string to a byte array.

```javascript
bytesFromBase64(base64: string): byte[];
```

### stringToBase64

Converts a string to a base64 string.

```javascript
stringToBase64(value: string): string;
```

### stringFromBase64

Converts a base64 string to a string.

```javascript
stringFromBase64(base64: string): string;
```

### streamToBytes

Converts a stream string to a byte array.

```javascript
streamToBytes(value: Stream): byte[];
```

### streamToBase64

Converts a stream to a base64 string.

```javascript
streamToBase64(value: Stream): string;
```


---

# Agent Instructions: Querying This Documentation

If you need additional information that is not directly available in this page, you can query the documentation dynamically by asking a question.

Perform an HTTP GET request on the current page URL with the `ask` query parameter:

```
GET https://docs.elsaworkflows.io/expressions/javascript.md?ask=<question>
```

The question should be specific, self-contained, and written in natural language.
The response will contain a direct answer to the question and relevant excerpts and sources from the documentation.

Use this mechanism when the answer is not explicitly present in the current page, you need clarification or additional context, or you want to retrieve related documentation sections.